Phases of the Moon

The revolution of the Moon around the Earth makes the Moon appear as if it is changing shape in the sky.  This is caused by the different angles from which we see the bright part of the Moon's surface.  These are called "phases" of the Moon.  Of course, the Moon doesn't generate any light itself; it just reflects the light of the Sun.  The Moon passes through four major shapes during a cycle that repeats itself every 29.5 days.  The phases always follow one another in the same order.  Below are pictures of the four major shapes and a description of each.

	New Moon: The lighted side of the Moon faces away from the Earth.  This means that the Sun, Earth, and Moon are almost in a straight line, with the Moon in between the Sun and the Earth.  The Moon that we see looks very dark.
	First Quarter: The right half of the Moon appears lighted and the left side of the Moon appears dark.  During the time between the New Moon and the First Quarter Moon, the part of the Moon that appears lighted gets larger and larger every day, and will continue to grow until the Full Moon.
	Full Moon: The lighted side of the Moon faces the Earth.  This means that the Earth, Sun, and Moon are nearly in a straight line, with the Earth in the middle.  The Moon that we see is very bright from the sunlight reflecting off it.
	Last Quarter: Sometimes called Third Quarter.  The left half of the Moon appears lighted, and the right side of the Moon appears dark.  During the time between the Full Moon and the Last Quarter Moon, the part of the Moon that appears lighted gets smaller and smaller every day. It will continue to shrink until the New Moon, when the cycle starts all over again.

1. What phase is the Moon closest to right now?
2. Go to this site.  When will there be a Full Moon this month?  When will there be a New Moon this month?
3. Based on the calendar at the above Internet site, and the fact that it takes about 29.5 days for the Moon Cycle to repeat, see if you can predict when the next Full Moon and New Moon will be (for help, use a calendar).  Go to the Space Academy and use the Moon Phase Applet to check your answers.
4. Now, repeat questions 2 and 3 for the First Quarter Moon and Last Quarter Moon.

There are also four other phases of the Moon sometimes used.  They are as follows: 
 

	This is known as a Waxing Crescent Moon.  This Moon can be seen after the New Moon, but before the First Quarter Moon.  The crescent will grow larger and larger every day, until the Moon looks like the First Quarter Moon.
	This Moon is known as a Waxing Gibbous Moon.  This Moon can be seen after the First Quarter Moon, but before the Full Moon.  The amount of the Moon that we can see will grow larger and larger every day.  ("Waxing" means increasing, or growing larger.)
	This Moon is called a Waning Gibbous Moon.  This Moon can be seen after the Full Moon, but before the Last Quarter Moon.  The amount of the Moon that we can see will grow smaller and smaller every day. ("Waning" means decreasing, or growing smaller.)
	This Moon is called the Waning Crescent Moon.  This Moon can be seen after the Last Quarter Moon and before the New Moon.  The crescent will grow smaller and smaller every day, until the Moon looks like the New Moon.

Do you feel you understand the Phases of the Moon?  Then take the Phases of the Moon quiz at NASA's StarChild Project website!